In the current conventional fuel evaporative control system, an operator of a vehicle is not aware if there is a malfunction in the purging process, whereby fuel vapors stored in the canister are not being purged into the engine induction system. Therefore, the only means to determine a malfunction is a visual inspection of the evaporative control system. If the canister is not purged, it will become saturated and fuel vapors that would normally be adsorbed by the adsorbent in the canister will be emitted into the atmosphere.
U.S. Pat. No. 4,962,744 issued Oct. 16, 1990 to Kouji Uranishi et. al. shows a method to detect a malfunction in the evaporative control system. It monitors the temperature inside the evaporative canister and then calculates the change in temperature when adsorbing and purging fuel vapor. U.S. Pat. No. 4,949,695 issued Aug. 21, 1990 to Kouji Uranishi et. al. is another method to detect a malfunction by comparing the pressure in the fill and/or purge passage with that of the pressure in the intake vacuum.